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25 yo male punched a street sign earlier in the day and was complaining of pain and decreased function. His hand is grossly swollen along the dorsal aspects of carpometacarpal joints 2-5. His fingers on the affected hand are fixed in extension and he cannot voluntarily move his fingers. He can tolerate only minimal passive motion of the MCP joints 2-5. Cap refill and sensation are all within normal limits. The following xrays were obtained:

What is the diagnosis?

What is the most appropriate treatment?​

DiagnosisRight Carpometacarpal 2-5 Dislocation

Most Appropriate TreatmentClosed reduction under sedation w/ and splinting and hand surgeon follow up outpatient.

BackgroundTypically carpometacarpal (CMC) fractures or dislocations are high velocity impact injuries, usually involving trauma or boxing. These injuries are uncommon and account for less than 1% of all hand injuries [1]. Fractures and dislocations of the CMC are sometimes recognized because of the associated swelling and overlapping metacarpals on radiographs. Dorsal displacement of the fifth CMC is most common but any CMC joint can be displaced in any plane of motion [2].

Making the DiagnosisThese injuries are commonly associated with trauma and a thorough secondary evaluation is essential. Patients with CMC fractures or dislocations typically present with significant swelling and lack of function. In these situations a high index of suspicion is necessary to make the diagnosis [3].

The physical exam will show significant swelling and lack of function. Ulnar deviation of the fifth phalanx is typical of a fifth CMC dislocation. Neurologic exam may also show weakness of the interossei and adductor pollicis which are innervated by the deep branch of the ulnar nerve, a nerve that may be compressed between the fourth CMC and associated soft tissue [4].

Radiographs are not always definitive as the metacarpals frequently overlap and obscure underlying anatomy [2].

The metacarpal cascade technique is an easy and quick method to evaluate for carpometacarpal (CMC) dislocation on radiographs. In a normal posterior anterior radiograph of a neutral wrist, lines superimposed through the central longitudinal axis of each metacarpal converge to a common point 2 cm proximal to the articular surface of the distal radius (Fig 1) [9]. An abnormal convergence indicates a CMC dislocation (Fig 2) [7].

Alternatively, the lateral radiographs can be used to determine ulnar sided CMC fracture dislocations through evaluation of the intermetacarpal angle. In this technique lines should be superimposed along the medullary canal of the index, long and small metacarpals. The angles between the index and small metacarpal (I-S IMA) and between the long and small metacarpal (L-S IMA) are measured. If either I-S IMA or L-S IMA is > 10º then the CMC fracture or dislocation should be considered [5].

Emergency Department TreatmentClosed reduction is usually achieved in the emergency department under procedural sedation or nerve block with manual manipulation. There are two techniques to attempt:

Place the affected hand in finger traps. Once muscles are relaxed, apply a longitudinal traction and pressure applied to the base of the affected CMC joints [6].

Manual traction, flexion and longitudinal pressure at the base of the CMC may be successful [7].

Place the patient in a dorsal-volar splint that should be worn for 2 weeks weeks. Refer to an orthopedic or hand surgeon in 2 to 3 days [7].

Hand Surgeon RecommendationsWhile these dislocations may be reduced in the emergency department, this may not be maintained as this injury is inherently unstable. In the event that the reduction is not maintained, operative intervention either with repeat closed reduction and percutaneous pinning or open reduction internal fixation (ORIF) can be performed at a later date. A small study by Prokuski and Eglseder determined that patients who were treated operatively 4 weeks after their CMC dislocation had similar long term outcomes relative to those who were initially treated surgically [8]. Consult with your hand surgeon regarding the best course of action.

ConclusionCMC dislocations can occur in any plane of motion and can be missed in the setting of a high impact trauma. A thorough secondary assessment is critical as is proper interpretation of the radiographs. The metacarpal cascade is a quick and easy way to assess for CMC disruption. Evaluation of intermetacarpal angle can also be helpful as anatomy can sometimes obscure the view of the CMC joints. Under adequate pain control and sedation a closed reduction can be performed in the ED. However, these dislocations are inherently unstable and may require pinning or ORIF. Ideally this surgery should be done as soon as possible but there are not any known long term disabilities associated with waiting several weeks.

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